Individual sensors are frequently used to measure a force or an acceleration in each of several axes of interest. For example, to measure acceleration along the X- and Y-axes, two sensors are used. One has its sensitive axis along the X-axis and the other has its sensitive axis along the Y-axis.
These sensors can be formed from micromachined silicon structures. In such sensors, a movable mass is positioned between two plates so that one capacitor is formed by one plate and the mass and a second capacitor is formed by the second plate and the mass.
The application of a force along a sensitive axis causes the mass to move relative to the plates, causing a change in the capacitances in the two capacitors of the differential capacitor. This causes a signal to appear on the mass that reflects the amount of acceleration. An accelerometer based on this principle and a process for fabricating such an accelerometer are described in commonly assigned U.S. Pat. Nos. 5,345,824 and 5,314,572, which are incorporated herein by reference.
As the mass in such an accelerometer (or other sensor) forms a single electric node, and is used to output a signal corresponding to the acceleration or force, it has proven difficult to measure acceleration or a force in more than one axis using one movable mass.
The present invention overcomes this and other problems as will be shown in the remainder of the specification referring to the attached drawings.